Aspects of the disclosure relate to mobile devices, and more particularly, a system and method for obtaining at least one bodily function measurement of a user operating a mobile device.
It is often desirable for a user to be aware his/her bodily function measurements. Recently, many individuals wear small portable devices capable of measuring their heart rate (HR) and other physiological information. One of the most popular techniques used by these devices to measure heart rate is photoplethysmography (PPG). The PPG method works well when heart rate is measured on an individual's finger. However, many of the small portable fitness devices are wearable electronics that are typically package in the form of a watch (e.g., smart watch), activity monitoring band (e.g., worn on the wrist), etc. However, the vasculature of the human wrist is such that the PPG signal measured at the wrist at least an order of magnitude weaker than when measured at the finger. Additionally, current wrist worn devices are subject to motion artifacts, further exacerbating this issue.
Motion artifacts can be caused by a variety of mechanisms. An example of such a mechanism is a small uncontrollable motion of human body components (e.g., muscle, bone, ligament, blood vessel, etc.) associated with the acts of living, such as breathing. Another example is blood “sloshing” in the blood vessels caused by motion of an individual's arm with varying acceleration, such as swinging arms when walking. Yet another example is the relative motion of the PPG sensor itself and blood-perfused tissue. Such mechanisms can dwarf the “useful” modulation of the PPG signal caused by the true heart beating. It is very challenging to separate the individual's actual HR from the modulation of the optical signal caused by the motion artifacts.
Accordingly, a need exists for a wearable heart rate PPG sensor that is immune to motion artifacts.